Hundreds of thousands of public sector employees, including police officers, lecturers and border control staff, will stage a day of protest against the government austerity programme on Thursday.

About 20,000 off-duty police officers are expected to March in central London and plan to wear a total of 16,000 black caps to mark projected job losses over the next four years.

At the same time public sector unions will hold their third one-day walkout in 12 months, led by the Public and Commercial Services (PCS) civil servants' union, health workers at the Unite union, teachers and lecturers at the University and College Union, the Nipsa civil servants' union in Northern Ireland and Royal Navy support staff at the RMT union.

More than 400,000 public sector employees could be involved in the walkout, with the PCS representing the largest bloc, with 250,000 members, followed by Unite, with 100,000.

The PCS general secretary, Mark Serwotka, said the strikes over changes to public sector pensions would show that "the tide has turned" against pension reforms. A national strike by around 1 million public sector workers on 30 November last year was followed by a series of outline agreements for civil service, health, education and local government employees. Pension reforms were included in the Queen's speech, despite opposition to changes that include pegging the public sector pension age to the state pension age and higher contributions.

However, major health, civil service and education unions have not backed the reforms, and Serwotka said he would urge the Trades Union Congress to reopen pension negotiations with the government.

Speaking before a rally in central London to mark the strikes, Serwotka said: "The significance of this strike is that the government clearly thought that 30 November was the end of it, and they are clearly trying to project the image that the issue is done. These strikes will show very clearly that this is not the case."

The PCS has played down the prospect of disruption at Heathrow airport, where it represents immigration control officers, despite the furore over queues in passport halls. The Home Office is expected to deploy its successful contingency operation, used twice last year, which involves drafting in security-cleared staff from the Home Office and the Ministry of Defence to man passport booths.

Tens of thousands of lecturers from at least 75 universities and university colleges and more than 270 further education colleges will take part in the walkout over changes to the teachers' pension scheme.

The changes are likely to cost lecturers between an extra £350 and £500 a year in pension contributions – a 50% rise. When the changes are introduced, in 2015, many will have to work until the age of 67 or 68, rather than 65.

Sally Hunt, general secretary of the University and College Union (UCU), which represents lecturers, said college and university staff were already seeing the impact of the government's pension changes.

"It is simply not fair for ordinary families to be to be bearing the brunt of the government's cuts while those at the top get tax cuts," she said.

Universities and colleges across England are taking part. Steve Storey, branch chairman of the UCU at Sunderland University, said lecturers in their 20s, 30s and 40s would be the ones to suffer from the changes. "A lot of lecturers, like myself, are going on strike and sacrificing a day of pay to protect the pensions of people in the future," he said.

Unite represents around 100,000 health staff, including radiologists and health visitors and some paramedics, with the likelihood that appointments will have to be cancelled or rescheduled.